Currently, a technology for obtaining visual information among five senses of a human is actively being developed. An essential technology for developing such a digital image implementing technology is an image sensor technology. The image sensor is a semiconductor device which converts an optical signal into an electrical signal. The image sensor may be classified into a CCD (charge coupled device) image sensor based on a silicon semiconductor and a CMOS (complementary metal oxide semiconductor) image sensor. Generally, the CMOS image sensor has lower unit cost of production and lower power consumption, easier integration of a periphery circuit on the same chip and a higher processing speed than those of the CCD image sensor. Therefore, in recent years, the CMOS image sensor has dominated the market while replacing the CCD image sensor.
The CMOS image sensor uses a silicon p-n junction photoelectric conversion device (photodiode) as a photo detection method. The CMOS image sensor is manufactured by integrating large number of silicon p-n junction photoelectric conversion device unit pixels in an array in order to obtain an image. Recently, in order to obtain an image resolution and a high quality image of the CMOS image sensor, a size of a unit pixel, that is, a size of a silicon p-n photoelectric conversion device unit pixel is reduced so that a technology development with a high integrated pixel structure is performed.